Abstract

The past two decades have seen a rise in the number of investigations examining the
health-related effects of religiously motivated fasts. Islamic Ramadan is a 28 - 30
day fast in which food and drink are prohibited during the daylight hours. The majority
of health-specific findings related to Ramadan fasting are mixed. The likely causes
for these heterogeneous findings are the differences between studies in the following:
1) the amount of daily fasting time; 2) the percentage of subjects who smoke, take
oral medications, and/or receive intravenous fluids; and 3) the subjects' typical
food choices and eating habits. Greek Orthodox Christians fast for a total of 180
- 200 days each year, and their main fasting periods are the Nativity Fast (40 days
prior to Christmas), Lent (48 days prior to Easter), and the Assumption (15 days in
August). The fasting periods are more similar than dissimilar, and they can each be
described as a variant of vegetarianism. Some of the more favorable effects of these
fasts include the lowering of body mass, total cholesterol, LDL-C, and the LDL-C/HDL-C
ratio. The Biblical-based Daniel Fast prohibits the consumption of animal products,
refined carbohydrates, food additives, preservatives, sweeteners, flavorings, caffeine,
and alcohol. It is most commonly partaken for 21 days, although fasts of 10 and 40
days have been observed. Our initial investigation of the Daniel Fast noted favorable
effects on several health-related outcomes, including: blood pressure, blood lipids,
insulin sensitivity, and biomarkers of oxidative stress. This review summarizes the
health-specific effects of these fasts and provides suggestions for future research.